Here's a real-time software ray tracing engine demo I did in C last year (named Folf-Ray). It was made to contrast pixel art and the feel of old PC games with more realistic lighting. While it was fun to work on, the CPU requirements would limit any indie game made with it, so I shelved it.
#gamedev

Here's a clip from an old NES demo of an engine I wrote in assembly. Working around all of the NES's hardware bugs made this quite a project! This demo just tests the engine's ability to handle a bunch of characters running basic AI with the music engine and everything else.
#nesdev